Developing a secure, un-hackable net

A
method of securely communicating between multiple quantum devices has been
developed by a UCL-led team of scientists, bringing forward the reality of a
large-scale, un-hackable quantum network.

To
date, communicating via quantum networks has only been possible between two
devices of known provenance that have been built securely.

With
the EU and UK committing €1 billion and £270 million* respectively into funding
quantum technology research, a race is on to develop the first truly secure,
large-scale network between cities that works for any quantum device.

"We're
in a technology arms race of sorts. When quantum computers are fully developed,
they will break much of today's encryption whose security is only based on
mathematical assumptions. To pre-emptively solve this, we are working on new
ways of communicating through large networks that don't rely on assumptions,
but instead use the quantum laws of physics to ensure security, which would
need to be broken to hack the encryption," explained lead author, Dr Ciarán Lee
(UCL Physics & Astronomy).

Published
in Physical Review Letters and funded by the Engineering and Physical
Sciences Research Council, the study by UCL, the University of Oxford and the
University of Edinburgh scientists details a new way of communicating securely
between three or more quantum devices, irrespective of who built them.

"Our approach works for a general
network where you don't need to trust the manufacturer of the device or network
for secrecy to be guaranteed. Our method works by using the network's structure
to limit what an eavesdropper can learn," said Dr Matty Hoban (University of
Oxford, previously University of Edinburgh).

The approach bridges the gap between the
theoretical promise of perfect security guaranteed by the laws of quantum
physics and the practical implementation of such security in large networks.

It
tests the security of the quantum devices prior to engaging in communications
with the whole network. It does this by checking if the correlations between
devices in the network are intrinsically quantum and cannot have been created
by another means.

These
correlations are used to establish secret keys which can be used to encrypt any
desired communication. Security is ensured by the unique property that quantum
correlations can only be shared between the devices that created them, ensuring
no hacker can ever come to learn the key.

The
team used two methods - machine learning and causal inference - to develop the
test for the un-hackable communications system. This approach distributes
secret keys in a way that cannot be effectively intercepted, because through
quantum mechanics their secrecy can be tested and guaranteed.

"Our
work can be thought of as creating the software that will run on hardware
currently being built to realise the potential of quantum communications. In
future work, we'd like to work with partners in the UK national quantum
technologies programme to develop this further. We hope to trial our quantum
network approach over the next few years," concluded Dr Lee.

The
team acknowledge that an un-hackable network could be abused in the same way
that current networks are, but highlight that there is also a clear benefit to
ensuring privacy too.